IGBT module construction

ABSTRACT

A hybrid vehicle includes a power unit communicating power between a turbine alternator, flywheel and traction motor. The power unit stores DC power in capacitors and places the power on a DC bus for use in driving the induction machines. Power transistors receive the DC power from the DC bus and are pulse width modulated to output a synthesized AC waveform. The power transistors include a support plate of thermally conductive material having a first surface supporting the transistor and a second surface forming a heat sink with cooling fluid. An electrical insulation layer is fixedly connected between the power transistor and the support plate on the first surface.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of pending application Ser. No.08/641,922, titled "IGBT Module Constructor" filed, May 2, 1996 by thesame inventors as in the present application, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to powertrain systems invehicles, and, more particularly, to a hybrid powertrain system in anautomotive vehicle.

2. Description of the Related Art

Since the invention of power vehicles, many different powertrain systemshave been attempted, including a steam engine with a boiler or anelectric motor with a storage battery. It was, however, the four-strokeinternal combustion engine invented by Otto in 1876, and the discoveryof petroleum in 1856 that provided the impetus for the modern automotiveindustry.

Although gasoline emerged as the fuel of choice for automotive vehicles,recent concerns regarding fuel availability and increasingly stringentfederal and state emission regulations have renewed interest inalternative fuel powered vehicles. For example, alternative fuelvehicles may be powered by methanol, ethanol, natural gas, electricityor a combination of fuels.

A dedicated electric powered vehicle offers several advantages:electricity is readily available; an electric power distribution systemis already in place; and an electric powered vehicle produces virtuallyzero emissions. There are several technological disadvantages that mustbe overcome before electric powered vehicles gain acceptance in themarketplace. For instance, the range of present electric poweredvehicles is limited to approximately 100 miles, compared to about 300miles for a gasoline powered vehicle. Further, the acceleration is abouthalf that of a similar gasoline power vehicle. There is, therefore, aneed in the art for a powertrain to provide an electric motor for anautomotive vehicle which is capable of performing as dynamically as aninternal combustion engine.

SUMMARY OF THE INVENTION

Objects of the invention include each transistor being designed as anassembly that is an integral part of a composite heat sink, or coldplate.

Another object includes the transistors being electrically isolated fromthe heat sink by a thermally conductive substrate.

Another object includes the geometry of two transistors connectedtogether combined with the DC bus bar assembly to minimize the parisiticloop inductances.

The invention includes a power transistor assembly comprising at leastone power transistor and a support plate of thermally conductivematerial having a first surface supporting the power transistor and asecond surface forming a heat sink with cooling fluid. An electricalinsulation layer is fixedly connected between the power transistor andthe support plate on the first surface.

Other objects, features and advantages of the present invention will bereadily appreciated as the same becomes better understood after readingthe subsequent description taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a hybrid vehicle.

FIG. 2 is a block diagram of a power train for the hybrid vehicle.

FIG. 3 is a schematic view of the power unit in the vehicle.

FIG. 4 is a perspective view of the power unit.

FIG. 5a is a plan view of a transistor module.

FIG. 5b is a side view of a transistor module.

FIG. 6 is an exploded view of the heat exchanger and AC bus.

FIG. 7 is an exploded view of the DC bus.

FIG. 8 is a cross sectional view of the assembled DC bus.

FIG. 9 is an exploded view of the DC cross strap.

FIG. 10 is a perspective view of the cross ties.

FIG. 11 is a perspective view of the traction motor AC bus.

FIG. 12 is a perspective of the flywheel AC bus.

FIG. 13 is a perspective of the turbine alternator AC bus.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring to FIGS. 1 and 2, a hybrid powertrain system is illustratedfor an automotive vehicle 20. The vehicle 20 is partially shown in a cutaway view illustrating a hybrid powertrain system 22 disposed within thechassis 24. The hybrid powertrain system 22 includes a gas poweredturbine engine 26, which in this example is fueled by liquefied naturalgas. The turbine engine 26 spins an alternator unit 28 to generateelectric power. It should be appreciated that in this example there aretwo alternators in the alternator unit 28 that run at different speeds,such as 60,000 rpm and 100,000 rpm, to produce electricity equivalent to500 horsepower. A flywheel 40 is provided for energy storage. A tractionmotor 32 receives power to move the vehicle 20.

A power management controller 30 controls power between the alternatorunit 28, turbine engine 26, traction motor 32 and flywheel 40. Themanagement controller 30 is in communication with the turbine engine 26and alternator unit 28, and manages the distribution of power from thealternator 28 to the traction or induction motor 32 and through a drivetrain, utilizing a three phase variable frequency alternating current(VFAC). In this example the traction motor 32 is an AC induction motor.The traction motor 32 transfers its energy to the drive train 40 todrive the automotive vehicle 20.

Therefore, when a user requires acceleration of the vehicle 20, a signalis produced and is communicated to the management controller 30. Themanagement controller 30 directs the alternator 28 and if necessary aflywheel 40, to supply power to the traction motor 32 which in turndrives the wheels 42. If the power need of the traction motor 32 is low,the management controller 30 directs the excess power capacity into theflywheel 40 for storage.

The hybrid powertrain system 22 also includes various critically placedsensors which are conventional and well known in the art. The outputs ofthese sensors communicate with the control system 30. It should also beappreciated that the automotive vehicle 20 includes other hardware notshown, but conventional in the art to cooperate with the hybridpowertrain system 20.

The peripheral machines, comprising the turbine alternator unit 28 andtraction motor 32 are all induction machines. The flywheel 40 is apermanent magnet machine. Power in the form of alternating current mustbe supplied to each electric machine 28,32,40 and may be generated orprovided by each electric machine 28,32,40. The management controller 30manipulates the power to form the necessary signals for each electricmachine 28,32,40 (i.e., frequency and magnitude) and provides thenecessary magnitude changes.

The system 22 also includes a power unit 112 for converting and storingpower and transferring same between the electric machines 28,32,40 basedon control signals from the management controller 30.

The power unit 112 can transfer power directly between all of the majorelectric machines 28,32,40 bidirectionaly with the 800 VDC bus as themedium of exchange. The 800 VDC bus is held constant primarily byabsorbing and generating power from and to the flywheel. The DCcapacitor bank is used to absorb and generate power for the amount oftime needed for the flywheel controller to respond and control the DCbus which is approximately 5 milliseconds. For transients longer than 5milliseconds a combination of the flywheel and the dump resistor circuitis used. The bidirectional power to the turbo alternators 28 is powerthat is sent into the alternator 28 from the DC bus through the powertransistors to excite the magnetic field required to generate EMF. Theresultant power flow is out of the generator and is rectified from AC toDC by the diodes 122 in the transistor modules 120 and coupled back 800VDC bus.

The bidirectional power flow to the permanent magnet flywheel motor isthe power unit 112 acts as a buck regulator (or a step-down regulator)in the motoring mode and a boost regulator (or a step up regulator) inthe generator mode since the back EMF of the flywheel motor is fixedproportionally to the flywheel speed. The combination of the flywheelmotor system and DC capacitor bank form an electromechanical battery orenergy accumulator. A low power external 800 VDC is connected to thepower management system and is used to slow charge the electromechanicalbattery by storing energy in the flywheel by slowly increasing theflywheel speed.

The gas turbine engine is started by transferring energy from theflywheel to through the power unit to the alternators which are now usedas a inductive drive motor machine to start the turbines. The managementcontroller 30 manipulates and controls the power unit 112 to selectivelytransfer the power based on various operating conditions of the vehicle,and to synthesize a sinusoidal current waveform to operate the electricmachines 28,32,40 at the desired levels. Alternating current waveformsare constructed from DC stored signals. For example, the power unit 112stores DC voltage at a nominal 800V. The turbine alternator unit 28requires ac power signals at 1500-2 kHz, the flywheel requires AC powersignals up to 10 kHz, and the traction motor 32 requires AC powersignals at 600-700 Hz.

A schematic diagram of the power unit 112 is generally illustrated inFIG. 3. As illustrated, the power unit 112 includes a plurality of powerswitches in the form of power transistors 114 connected between theelectric machines 28,32,40 and a DC energy storage assembly in the formof a capacitor bank 116. The power transistors 114 switch power to eachof the electric machines 28,32,40 from the capacitor bank 116, and alsoswitch power from these machines to the capacitor bank 116. Thecapacitor bank 116 stores pulsating DC voltage levels at a nominal 800volts (±50V.). Connected between the capacitor bank 116 and the powertransistors 114 is a DC bus 118 which communicates the DC power storedin the capacitor banks 116 to and from the power transistors 114. Assubsequently discussed, the gates of the power transistors 114 arecontrolled such that synthesized AC power signals are sent to each ofthe electric machines 28,32,40 through pulse width modulation. In turn,AC power which is produced by the alternator unit 28 is rectified by thediodes mounted with power transistors 114 and is supplied to thecapacitor bank 116 via the DC bus 118.

The power transistors 114 are comprised of a plurality of insulated gatebipolar transistors (IGBT) which, as commonly known in the art, are ahybrid between a bipolar transistor and a MOSFET wherein an insulatedgate receives a voltage controlled signal which controls a large outputcurrent flowing through the transistor 114. The transistors 114 are partof a transistor module 120 illustrated in FIG. 5a.

Each transistor module 120 is comprised of six separate transistors 114and twelve diodes 122 connected on a common board forming the module120. The numerous transistors 114 and diodes 122 are utilized to sharethe high current flowing through the power unit 112. The transistors 114are each connected to a free wheeling diode 122 across theircollector/emitter. A dampening resistor 123 is connected to the gate126. The transistors 114 are connected in an H-bridge configuration toallow the production of three-phase AC signals. The H-bridge iscomprised of six transistor modules 120 connected as illustrated in FIG.3. In this arrangement, pairs of transistor modules 120 forming onephase have a common emitter and collector providing or receiving the ACsignal at their common collector/emitter point, whereas the other of theemitter and collector of the pair are connected to opposite polaritiesof the DC bus 118. Therefore, there are three pairs of transistormodules 120 producing the three-phase output signal. The gates 126 ofthe transistors 114 are connected to a gate drive assemblies 128, assubsequently discussed. The gate drive assemblies 128 pulse widthmodulate the transistors 114 to synthesize the AC waveform by switchingthe pairs on and off.

The traction motor 32 utilizes eighteen (18) transistor modules 120, theflywheel 40 utilizes twelve (12) transistor modules 120, and thealternator unit 28 utilizes twelve (12) transistor modules 120 (six foreach alternator).

The transistor modules 120 are connected to a fluid cooled cold-plate,which will be referred to as the heat exchanger assembly 130. The directconnection between the transistor modules 120 and the heat exchangerassembly 130 provide optimal cooling of the transistors 114 due to theswitching and current considerations of the transistor modules 120.

The transistor modules 120 include a support plate 132 which is indirect contact with the cooling fluid of the heat exchanger assembly130. The plate 132 is generally rectangular in shape and includes aplurality of cooling fins 134 extending from an outward surface thereof.The fins 134 extend longitudinally across the surface in the directionof coolant flow across the module 120 i.e., same direction of power flowthrough the module 120. The fins 134 provide turbulent flow through theexchanger 130 of the fluid with modest pressure drop but high thermaltransfer characteristics. An opposing supporting surface 135 supportsthe transistors 114 in thermal contact therewith. The support plate 132is preferably made of silicon carbide to enhance cooling conduction andto obtain a thermal coefficient of expansion similar to silicon (that ofthe transistors 114). The silicon carbide plate 132 is machined oralternatively cast to form the fins 134 and is over plated with gold. Anelectrical insulation layer 136 is connected by solder to the supportplate 132. The insulation layer 136 comprises DBC (direct bond copper)which is formed by a layer of copper, aluminum nitride, and copperheated to melt and fuse the copper to the ceramic substrate. The thermalconductivity is high in this layer 136 (similar to aluminum), and thelayer 136 can be soldered at the two outer copper surfaces. Asillustrated in FIG. 5a, six separate areas are formed by the insulationlayer 36 (two for the transistors 114 and four for the contact pads146). The integrated circuit chip (silicon) forming the transistors 114is soldered to the copper surface of the electrical insulation layer136. Each chip or die 114 represents one transistor operating at 75Amperes.

The module 114 includes raised contact pad 146 connected to thecollectors and emitters of the transistors 114 by suitable wire leadconnections 147. The contact pads 146 are formed of ductile copperstrips 148 to allow some bending and flexibility thereof for connection.This will provide suitable connection when the connection surfaces arenot coplanar within small tolerances with all of the contact pads 146.The strips 148 include a resilient bond 150 therein to allow for theextension and retraction of the contact pads 146 to ensure the requiredelectrical contact. The strips 148 include ends 149 which are solderedto the module 120 on the electrical insulation layer 136. The supportplate 132 includes a plurality of fastening apertures 154 extendingtherethrough for mounting, as subsequently described.

In each transistor module 120, either the collectors or emitters areconnected to the DC bus 118 at the contact pads 146 on one side of themodule 120. The strips 148 are connected by the wire leads 147 to theelectrically conducting DBC layer 136, and the transistor chip 114contacts the DC signal on its bottom die surface.

The heat exchanger assembly 130 provides cooling of the transistormodules 120, along with other components of the power unit 112. The heatexchanger assembly 130 includes a first frame member 160 having aplurality or matrix of open windows 162 therein. The windows 162 receivethe transistor modules 120 in sealed connection therewith. A sealingO-ring 164 is placed between the support plate 132 of the transistormodules 120 and the window 162. Frame walls 163 surround the windows 162and provide a flange to support the O-ring seal 164. The heat exchangerassembly 130 also includes a base plate 166 connected to the first framemember 160 and spaced therefrom establishing a first cavity to allowwater to flow between the base plate 166 and the frame member 160. Thefluid flowing in the cavity thereby flows through the fins 134 of thetransistors modules 114 to aid in cooling thereof. The first framemember 160 also includes fins 161 extending into the cavity which alignwith the fins 134 of the transistor modules 120. In the preferredembodiment, the heat exchanger 130 also includes a second frame member170 opposing the first frame member 160 about the base plate 166 andoperatively secured with the base plate 166 and the first frame member160. The second frame member 170 is spaced from the base plate 166 toestablish a second cavity therebetween for allowing fluid to flowtherethrough. Similarly, fins are provided on the interior surface ofthe frame.

A fluid inlet 172 is connected to either of the first or second framemembers 160,170, and a fluid outlet 173 is secured to the other of thefirst or second frame members 160,170. In the preferred embodiment, theinlet 172 is connected to the first frame member 160, and the outlet 173is connected to the second frame member 170. The flow is parallelthrough the heat exchanger 130. The end of the base plate 166 oppositethe inlet 172 and outlet 173 end is provided with are fluid openings 171to allow fluid to flow from the first cavity to the second cavity. Theframe members 160,170 and base plate 166 are generally rectangular inshape. The perimeter of the frame members 160,170 and base plate 166include a plurality of fastening apertures 174 therethrough forreceiving suitable fasteners 175 for connecting the frame members160,170 and base plate 166 to one another. Furthermore, each of thefirst and second frame members 160,170 include a plurality of supportposts 178 extending outwardly from the cross points of the frame walls163 between the corners of adjacent windows 162. The support posts 178are for mounting in the DC bus 118, as discussed subsequently. Also,included are mounting apertures 179 extending into the outer edge of theperimeter wall of the base plate 166 for mounting the heat exchanger 130to a chassis housing 300, as subsequently discussed.

The windows 162 are formed in a matrix pattern within each of the framemembers 160,170. In the preferred embodiment, the matrix is formed by3×8 windows. The first frame member 160 includes a mounting plate 176connected in place of five (5) of the windows 162 to allow for mountingand cooling of additional components other than the transistor modules114. The windows 162 are formed in the remainder of the first framemember 160. All of the matrix is comprised of windows 162 in the secondframe member 170.

The transistor modules 120 are mounted to each of the frame members 160with the contact pads 146 extending outwardly from the heat exchangerassembly 130. Therefore, the transistor modules 120 are loaded from thecavity side of the frame members 160,170 with the O-ring seals 164therebetween. Fasteners connect the transistor modules 114 to the framemembers 160,170. In the preferred embodiment, the second frame member170 holds twenty-four (24) transistor modules 120, and the first framemember 160 holds eighteen (18) transistors modules 120. A remainder ofthe windows 162 not filled by a transistor module 120 is utilized for adump resistor 182, which is used for dumping power over a predeterminedlimit from the DC bus 118.

The DC bus 118 comprises two DC buses 118a,118b identically formed andeach including a positive and negative half. Therefore, the generalstructure of the DC bus 118 will be described, it being understood thatit is applied to both separate buses 118a,118b. The DC bus 118 includesa first conducting plate 190 and a second conducting plate 191. Aninsulation layer 192 is sandwiched between the two plates 190,191. Theplates 190,191 and the insulation layer 192 are laminated to one anotherforming a thin conducting plane. The first conducting plate 190 formsthe positive DC signal and the second conducting plate 91 forms thenegative or reference DC signal. Each of the first and second conductingplates 190,191 include fluid passages 194 extending within the plates190,191 allowing fluid to circulate therein for cooling purposes. Eachof the plates 190,191 include a fluid inlet 195 and a fluid outlet 196extending longitudinally outwardly from opposite ends of the plates190,191 and along a common side thereof. The bus fluid inlets 195 forboth plates 190,191 are both on one end of the buss 118 and the busfluid outlets 196 are on an opposing end of the bus 118 for allowingcoolant or water to be pumped therethrough. The inlet/outlet pair195,196 on the first plate 190 is on an opposing side from the pair195,196 of the second plate 191 (see FIG. 7).

Each of the plates 190,191 is formed by first and second conductingsheets 198,199 with a corrugated material 200 therebetween. The sheets198,199 and corrugated sheet material 200 are brazed sealed to oneanother forming an enclosed cavity to allow the fluid to passtherethrough. An aluminum material is utilized for each of the sheets198,199 and corrugated sheet 200. The flow through the plates 190,191 isin a serpentine manner with longitudinal openings 202 in each plate190,191 separating each channel and change in direction of flow. Thecorners 204 in serpentine flow pattern are provided by 45° straightchannels as illustrated in FIG. 7.

The bus inlets 195,196 are connected to the heat exchanger 130 toreceive fluid flow. The heat exchanger 130 includes a pair of elongatedfluid openings 206 near the outer corners of the first frame 160 and atthe same end as the exchanger inlet 172 to pump coolant to the inlets195 of the bus plates 190,191 of the upper DC bus 118a. The heatexchanger 130 includes a second pair of elongated openings 208 near theouter corners of the first frame 160 at the end opposite the exchangerinlet 172 to receives the return flow of fluid from the upper DC bus118a. Similarly, the second frame 170 of the heat exchanger includespairs of elongated openings 210 for supplying and circulating fluidthrough the lower DC bus 118b. Therefore, a single fluid inlet andoutlet to the heat exchanger 130 provides circulating cooling fluid forboth the heat exchanger 130 and the DC bus 118.

The first and second conducting plates 190,191 include a plurality oflongitudinal openings 202 extending between the serpentine fluid flowpaths. There are provided parallel rows of the openings 202. The DC bus118 provided to allow direct contact to the transistor modules 120 on afirst side thereof and direct contact to the capacitor banks 116 on thesecond side thereof. In both cases, both positive and negative sidecontacts 212,214 must be provided to each of the surfaces, i.e. to eachof the capacitors 116 and to each of the transistor modules 120. Theopenings allow for contacts from one plate to extend through the otherplate, and vise versa. Each of the conducting plates 190,191 include aplurality of contact posts 212,214 extending on both first and secondsides of the plates 190,191 and perpendicular therewith. The contacts214 extending on the side of the plates 190,191 adjacent the insulationlayer 192 are positioned in the openings 202 of the other of the plates190,191. Therefore, when viewing a first side of the first conductingplate 190 (See FIG. 7), the plate 190 includes contacts 212 extendingoutwardly from the surface, and within the openings provided in theplate 190 are extended opposite polarity contact posts 214 through theinsulation layer 192 from the second conducting plate 191. The outersurface of the second conducting plate 191 is also similarly orientedwith the positive and negative conducting posts 212,214 both extendingon one side. The positioning of the contact posts 212,214 depends on thepositioning of the transistor modules 120 and the brackets for holdingthe capacitor banks 116. It can be appreciated that both the positiveand negative DC signals are required off both outward surfaces of the DCbuses 118a,118b. Both DC buses 118a,118b are similarly formed, with thegeometry or positioning of the contact posts 212,214 varying dependingon necessary connections.

The plates 190,191 include a plurality of holes 216 formed therein andextending through the buses 118a,118b to be aligned with the connectionposts 178 of the cross points on the heat exchanger 130. The heatexchanger 130 and the DC buses 118a,118b are mounted to one another forstructural ridgity at these holes by suitable fasteners.

The longitudinal side edges of the DC bus 118, i.e. each of the plates190,191, include contact pads 218,220 formed therein. The perpendicularcontact pads 218,220 are perpendicular to the plane of the DC bus. Thesecontact pads 218,220 allow for interconnection between the two buses118a,118b, as subsequently discussed.

The first and second bus members 118a,118b are spaced from one anotherabout the heat exchanger 130. A plurality of conducting strap members222 interconnect the first and second buses 118a,118b. The conductingstrap members 222 include first and second strap plates 223,224electrically insulated from one another and secured to one another. Afirst of the strap plates 223 is connected to the positive bus plates190 and a second of the strap plates 224 is connected to the negativebus plates 191. The strap plates 223,224 are comprised of generallyplanar, wide thin sheets sandwiched against one another. An insulationsheet 225 of material is provided and laminated between the strap plates223,224 to isolate the opposite polarity signal on the plates 223,224.The strap plates 223,224 include first and second ends. The first andsecond ends include planar contact pads 226,228 extending outwardly fromeach end. The contact pads 226 of the first plate 223 include a shoulder227 formed therein off set from the plate so that the contact pads 226of the first and second plates 223,224 are coplanar when assembled. Thecontact pads 226,228 are fixedly connected to the perpendicular contactpads 218,220 extending from the two bus members 118a,118b. This allowscurrent to flow through the strap members 222 to each of the bus members118. The strap members 222 are comprised of sheet aluminum materialcoated on their outer surface by a gold layer to increase conductivity.The strap members 222 are symmetrical.

The bus members 118 and straps 222 are laminated to keep the inductanceof the bus system at a minimum. This keeps the voltage spikes duringswitching low. It also allows a reduction of capacitance required tostabilize the bus 118.

There is provided approximately one half inch clearance between thesurface of the heat exchanger 130 and the DC bus 118. Within this spaceare located various ac bus bars for contacting the transistor modules120 and directing the output current therefrom to the electric machine28,32,36 to be driven by the ac signals.

The power unit 112 includes cross ties 230 as illustrated in FIG. 10.The cross ties are comprised of an aluminum sheet of material cut out tohave four (4) symmetrical arms 232 extending therefrom with outer endsof the each arm 232 including a mounting aperture 233 and the centerpoint of the cross tie includes a mounting aperture 234. As can beunderstood, there are two (2) transistor modules 120 which form onethird of the H-bridge which drive the induction machines in three phase.As illustrated in FIG. 3, each pair of transistors have a common emitterand collector connected to one another. The cross ties 230 form thisinterconnection as illustrated. Each of the modules 120 forms 1/6 of theH-bridge and is connected to its pair. For example, all of thecollectors of transistor module 120a are connected to all of theemitters of transistor module 120b by the cross tie 230 to provide asingle out put at center aperture 234 of one phase of the ac signal. Thecross ties 230 are constructed of an aluminum material with gold platingas with the DC strap plates 222.

The turbine alternator requires a single pair of transistor modules 120for each phase as is illustrated in the drawings, i.e., six transistormodules 120. The flywheel requires two (2) layers of the H-bridgetransistors modules 120 for each transistor illustrated in the FIG. 3.Therefore, four (4) transistor modules 120 are used to drive one phase.In the case of the traction motor, there are three (3) transistormodules 120 for each transistor illustrated in FIG. 3. In other word,six (6) transistor modules 120 drive one phase of the traction motor.The amount of transistor modules 120 used is due to current requirementsof the machines.

The ac bus bars include a bus bar assembly for each electric machine28,32,40. The bus bar assemblies contact the respective cross ties 230and communicate the ac signals to the respective electric machines28,32,40. Each bus bar assembly includes one bus bar for each phase ofthe three phase signal. In the case of the traction motor, since thereare three (3) transistor modules for each of those illustrated in thegeneral FIG. 3, there is in effect six (6) transistor modules 120 whichproduce one phase of the ac signal. Therefore, the traction motor busbar assembly 240 contacts three (3) cross ties in order to produce onephase of the ac signal to the traction motor 32. This is accomplished byusing a pair of connecting plates 242,243. A first plate 242 includesthree apertures 244 for connection with three cross ties 230. The firstplate 242 includes a pair of center intermediate apertures 246 equallyspaced between the three 244. A second plate 243 is electricallyinsulated from the first plate by an insulation layer 248, except at theintermediate apertures 246 which conduct the signal from the first plate242 to the second plate 243. The second plate 243 includes a centerconnecting output aperture 250 to provide the single phase ac signal. Atransmitting bus bar 252 connects at the center point 250 of the secondplate 243 to connect the signal directly to the traction motor 32. Thecross strapping shown in FIG. 11 is to equalize the length of theindividual phases.

In regard to the flywheel, there are two (2) layers of the transistors120 for each illustrated in the general FIG. 3. Therefore, there are two(2) cross ties 230 which are interconnected by a first layer AC bus bar254 to provide one phase of the ac signal driving the flywheel 40. Atransmitting bus bar 256 connects the first layer bus bar to theflywheel 40.

In the case of the turbine alternator unit 28, the ac bus bar 260contacts a single cross tie 230 to provide a single phase of AC power. Asingle bus bar 261 for each phase is used and connected only to a singlecross tie 230. Therefore, three bus bars 261 are utilized to drive oneof the turbine alternators 28 for a three phase signal.

The intermediate bus bars are comprised of a single bar with geometry toevenly pull signals from each cross tie 230 contact. Each of thetransmitting bus bars 252,256,260 are comprised of multi layer sheets ofbars stacked on each other (See FIG. 11) and laminated and having thesame geometry and distance for each layer to insure symmetry of thesignal. In the preferred embodiment, five (5) bars are utilized toprovide the AC transmitting bus for a single signal for the flywheel 36and traction motor 32. This allows 700 Amps to be transmitted. Each ofthe frequencies at which the AC signal is operated, skin effect occurswhereby the signal is carried on the outside surface of the conductor.Therefore, by using a plurality of sheets of bars, higher signal levelsand signal response may be obtained. Each of the bars comprising a busis laminated together to provide a single unit. The turbine alternator28 uses single layer of bar.

The geometry of the AC bus bars is dependent upon space requirementswithin the power unit. In general, it is preferred to optimize width ofthe bars and shortness in distance to the driver machine.

The capacitor banks 116 are connected on the outer sides of the both ofthe DC buses 118a,118b, i.e., there are two (2) capacitor banks116a,116b. Each capacitor 270 is a metalized poly propylene filmcapacitor with low dissipation factor; each can carry 30 Amps and are 23mF. The capacitor banks 116 are comprised of a plurality ofcylindrically shaped capacitors 270 mounted to a plurality of mountingbracket 270 connected to the DC buses 118a,118b. The positive andnegative contact posts 212,214 extending from the DC bus 118a,118b areconnected to the L-shaped brackets 272. The base 273 of the L-shapedbracket is connected to the respective of the DC bus control posts212,214 wherein the perpendicular extending side includes apertures 274therein to receive ends of the capacitors 270. A pair of brackets 272 islaminated to each other with an insulation layer 276 therebetween. Oneof the brackets 272b connects to the negative DC bus plate 191 and theother of the brackets 272 connects to the positive DC bus plate 190.Each capacitor 270 is connected between positive and negative brackets272. A pair of brackets 272 is connected between rows of capacitors 270wherein one of the brackets 272a is positive and one of the brackets272b is negative. On the upper side of the power unit 112 there areconnected forty-eight (48) capacitors 270 between multiple pairs of thecapacitor brackets 272. On the lower capacitor bank 116b there areconnected twenty-four (24) capacitors 270 in a staggered arrangement. Indesign, the capacitance is made to be maximized with consideration ofthe space available. Therefore, more capacitors 270 could be used ifmore space was available.

Connected to the outer sides of the capacitor banks 116a,116b are thegate drivers 128. There is one gate driver 128 for each transistormodule 120. The gate driver 128 is comprised of a circuit board 280 withappropriate conductors and circuitry thereon. The gate drivers 128receive a control signal from the management controller 30 to drive thetransistors 114 at the established pulse width modulation to output theac signals. The gate drivers 128 are positioned in three rows on theoutside and a center row within the upper capacitor bank 116a, and onthe bottom of the lower capacitor bank 116b. Positioning is merely forcompact space requirements and to situate the drivers as close to itsrespective transistor module 120 as possible. Each of the leads from thegate drivers 128 is approximately three (3) to four (4) inches long andconnected to its respective transistor module 120. It is important thatthe conduction length be equivalent for each gate driver to ensureproper firing of the respective transistor module 120.

The remainder of the space on the heat exchanger absent the windowsprovides for connection of a 800 to 24 volt DC convertor 500 which isthereby liquid cooled by the heat exchanger 130. In the remainingpositions are located three (3) fluid pump electric drives, one for theheat exchanger 130, and the remaining two (2) for the electric machines28,32,40.

The power unit 112 includes a housing 282 for supporting each of theinternal components. The housing 282 is provided as an integrated unitwhen assembled with the power unit 112 and management controller 30which may be simply placed as a whole unit in the vehicle 20 and removedtherefrom. The housing 282 includes two opposing longitudinal side walls283,284 having fastening openings 285 extending along the center thereofalong the longitudinal length. The fastening openings 285 receivesfasteners which are connected to the mounting apertures 179 on the heatexchanger 130. By this method, the heat exchanger 130 and DC 118 and ACbuses are connected within the housing 282. The housing 282 alsoincludes an integrally connected end wall 286 providing outputsconnections at a first end. A second end wall 287 opposing the first endwall provides additional output and input connections. A divider wall288 is secured and positioned within the housing 282 to section off apart of the internal housing for the management controller 30 forEMI/RFI protection of the controller 30. Once the heat exchanger 130 andbuses and capacitor banks 116 and gate drives 128 are assembledtogether, the entire unit 112 is place within the housing 232 andsecured by the fasteners to the housing 232. Upper and lower walls maybe secured thereto to form an enclosed housing 232 which may then besimply placed and removed from the vehicle 20 while making only theexternal connections. The power density in the housing 232 is maximizedto 400 w/inch³. The housing is formed of carbon fiber composite.

The present invention has been described in an illustrative manner. Itis to be understood that the terminology which has been used is intendedto be in the nature of words of description rather than of limitation.

Many modifications and variations of the present invention are possiblein light of the above teachings. Therefore, within the scope of theappended claims, the present invention may be practiced other than asspecifically described.

What is claimed is:
 1. A power transistor assembly comprising:at leastone power transistor; a support plate of thermally conductive materialhaving a first surface supporting said at least one power transistor anda second surface having a plurality of cooling fins extending outwardlyin direct contact with cooling fluid; an electrical insulation layerfixedly connected between said power transistor and said support plateon said first surface; and a plurality of contact pads supported by saidsupport plate and electrically connected to said power transistor, saidcontact pads being formed of resilient strip of material with a bendformed therein to allow connection to external members of varyingdistances from said support plate.
 2. A power transistor assembly as setforth in claim 1 wherein said insulation layer is comprised of athermally conductive substrate.
 3. A power transistor assembly as setforth in claim 2 wherein said insulation layer includes said thermallyconductive substrate and copper layers fixedly connected on opposingsides of said thermally conductive substrate.
 4. A power transistorassembly as set forth in claim 3 wherein said insulation layer issoldered to said support plate.
 5. A power transistor assembly as setforth in claim 4 wherein said support plate comprises aluminum filledsilicon carbide.
 6. A power transistor assembly as set forth in claim 4wherein at least one of said contact pads is connected to a collector ofsaid transistor, and including contact leads extending from said contactpad to said copper layer.
 7. A power transistor assembly as set forth inclaim 6 wherein at least one of said contact pads is connected to anemitter of said transistor, said transistor connected by electricalleads to said contact pads.
 8. A power transistor assembly as set forthin claim 6 wherein said transistors comprise insulated gate bipolartransistors, each of said bipolar transistors having an emitter and acollector with a free wheeling diode connected across said emitter andsaid collector.
 9. A power transistor assembly comprising:at least onepower transistor; an integral support plate of thermally conductivematerial having a first surface supporting said at least one powertransistor and a second surface having a plurality of integral coolingfins extending outwardly in direct contact with cooling fluid; anelectrical insulation layer fixedly connected between said powertransistor and said support plate on said first surface, said electricalinsulation layer directly contacting said power transistor for heattransfer.